Vocal Shapes turns the tone of your voice into a beautiful graphical shape. Touching the screen freezes the image.
The sharpness of the image corresponds to the steadiness of the vocal tone. Therefore, it is a good tool for examining the quality of a singing voice. The richer the harmonic content of the tone, the more complex shapes arise.
Also try inputting musical instruments, buzzers, bells, electric shavers… anything that emits a steady tone. You might learn something about the nature of sound waves!
Technically, it is a Lissajous diagram of the input signal and its Hilbert transform.
The app is priced at $0.99.